The Universal Mobile Telecommunications Systems (UMTS) network architecture, illustrated in FIG. 1, includes a core network (CN) 2, a UMTS Terrestrial Radio Access Network (UTRAN) 3, and at least one User Equipment (UE) 18, (only one UE 18 being shown for simplicity). The two general interfaces are the Iu interface between the UTRAN and the core network as well as the radio interface Uu between the UTRAN and the UE.
The UTRAN consists of several Radio Network Subsystems (RNSs) 10, 11. They can be interconnected by the Iur interface. Each RNS 10, 11 is divided into a Radio Network Controller (RNC) 12, 13 and several base stations (Node Bs) 14-17. The Node Bs 14-17 are connected to the RNCs 12, 13 by the Iub interface. One Node B 14-17 can serve one or multiple cells.
The UTRAN 3 supports both FDD mode and TDD mode on the radio interface. For both modes, the same network architecture and the same protocols are used.
Communication between the Node Bs 14-17 and the UEs 18 over the radio interface Uu is conducted using a Radio Interface Protocol. The Radio Interface Protocol Stack architecture is illustrated in FIG. 2. As those skilled in the art would realize, the design of the Radio Interface Protocol Stack 20 is divided into three layers: the physical layer (L1) 21, the data link layer (L2) 22, and the network layer (L3) 23. L2 is split into four sublayers: the Medium Access Control (MAC) 24, the Radio Link Control (RLC) 25, the Broadcast/Multicast Control (BMC) 27, and the Packet Data Convergence Protocol (PDCP) 26.
L3 23 contains the Radio Resource Control (RRC) 28. The RRC handles the control plane signaling of L3 between the UTRAN 3 and the UEs 18. It is also responsible for configuration and control of all other protocol layers in the UTRAN 3 and for controlling the available radio resources. This includes assignment, reconfiguration and release of radio resources, as well as continuous control of the requested Quality of Service.
The Radio Link Control (RLC) layer 25 provides transparent, unacknowledged or acknowledged mode data transfer to the upper layers. The acknowledged mode transfer uses a sliding window protocol with selective reject-automatic repeat request.
The MAC layer 24 maps the logical channels of the RLC 25 on the transport channels, which are provided by the physical layer. The MAC layer 24 is informed about resource allocations by the RRC 28, and mainly consists of a multiplexing function. The priority handling between different data flows, which are mapped onto the same physical resources, is also done by the MAC layer 24. The function and operation of the BMC 27 and the PDCP 26 are well known to those of skill in the art and will not be explained in greater detail herein.
The physical layer 21 is responsible for the transmission of transport blocks over the air interface. This includes forward error correction, multiplexing of different transport channels on the same physical resources, rate matching, (i.e., matching the amount of user data to the available physical resources), modulation, spreading and radio frequency RF processing. Error detection is also performed by the physical layer 21 and indicated to the higher layers 22, 23.
The data flow through L2 22 is shown in FIG. 3. The higher layer Protocol Data Units (PDUs) are passed to the RLC layer 25. In the RLC layer 25, the Service Data Units (SDUs) are segmented and concatenated. Together with the RLC header, the RLC PDUs are built. No error detection code is added in the RLC layer 25. For transparent-mode RLC, no segmentation on the RLC layer 25 is performed and neither the RLC header nor the MAC header are added to higher layer PDUs.
In the MAC layer 24, only a header is added. This header can contain routing information which describes the mapping of logical channels to transport channels. On common channels, a UE identification can also be included.
In L1 21 (the physical layer), a CRC is added for error detection purposes. The result of the CRC check in the receiver is passed to the RLC layer 25 for control of retransmissions.
In current UMTS TDD or FDD systems, a radio resource control service data unit (RRC-SDU) may be sent in RLC transparent, unacknowledged or acknowledged modes between the UTRAN-RRC and the UE-RRC. The acknowledged mode will not be discussed hereinafter. However, when an RRC-SDU is transported in the transparent or unacknowledged modes, the RLC and MAC layers of the receiving side are not aware of the RRC-SDU. Therefore, any errors in the received RRC-SDU caused during transmission or by other sources, must be performed at the RRC layer, instead of at the lower layers.
The RRC-SDU may be transmitted in several individual segments known as transport blocks (TB). An example of an RRC-SDU is the broadcast control channel system information blocks (BCCH-SIB).
In the case of the BCCH-SIB, from the UTRAN-RRC to the UE broadcast control functional entity (UE-BCFE), TBs associated with this SIB are repeatedly retransmitted. SDU version indications are identified by “value tags”. When the value tag does not change, the UE 18 assumes that the UTRAN is repeatedly sending identical BCCH-SIBs. If there are changes in the BCCH-SIB transmitted from the UTRAN 3, the UTRAN 3 uses the value tag to indicate to the UE 18 that there has been a change. Scheduling information, when the TBs of a BCCH-SIB should arrive at the UE 18, and the version of the BCCH-SIB, are known to the UE 18 in advance of transmission from the UTRAN 3.
FIG. 4 is an illustration of the UE 18 receiving an L1 SDU. The SDU comprises the TB, which carries, for example, the BCCH-SIB; and a CRC, which is used by L1 of the UE 18 to perform transmission error detection. As illustrated, the TB may also include the system frame number (SFN), as is the case for a TB of the BCCH-SIB, which indicates the time when the TB should arrive at the UE 18. Alternatively, for a TB that does not explicitly contain the SFN, the SFN of arrival can be derived by L1 from physical layer timing. L1 of the UE 18 passes the TB, SFN and CRC result to the higher layers. However, since the RLC and MAC layers 25, 24 operate in transparent mode for broadcast channel (BCH) data, the TB is passed to the RRC layer.
Since TBs are often transmitted between the UE 18 and the UTRAN 3 in a fading environment, transmission of TBs is associated with a targeted probability of successful transmission/reception, for example ninety-nine percent (99%). If a BCCH-SIB consists of a large number of TBs, the probability of correctly receiving all of the TBs of a BCCH-SIB is approximated at 0.99 raised to the power of the number of TBs. For example, a BCCH-SIB of a broadcast control channel (BCCH) may need more than ten TBs to transmit; in this case, the probability of the UE 18 successfully receiving the BCCH-SIB is (0.99) to the 10, which is less than ninety percent (90%). Accordingly, the probability of successful reception of the BCCH-SIB decreases as the number of TBs increases.
In UMTS TDD or FDD systems, the time to successfully receive the SIBs determines the performance for many system functions. Additionally, to maintain proper performance of these system functions, SIB repetition rates may have to be increased to compensate for failed transmissions, which reduces radio resource efficiency and utilization.
FIGS. 5 and 6 are an illustration and a flow diagram, respectively, of a current method used for successfully receiving an RRC SDU transmitted by the UTRAN 3 to the UE 18. As shown, the UE-BCFE receives the RRC-SDU (Step 60) which, for purposes of this example, comprises 9 TBs, labeled from SFN=2 to SFN=18 at a repetition rate of 64 frames. The UE-BCFE reads the RRC-SDU and determines if there is a TB in error or missing from the RRC-SDU (Step 61). For purposes of this example, SFN 10 is assumed to have an error. Since an error exists in the received RRC-SDU, the UE-BCFE discards the entire RRC-SDU and waits the repetition rate, i.e. 64 frames, to receive another RRC-SDU carrying the same information (Step 62). Once again the UE-BCFE receives the RRC-SDU, comprising 9 TBs, labeled from SFN=66 to SFN=82 (Step 63), and determines if an error is present (Step 61). In this example, SFN 70 (SFN 6+64 (repetition rate)) has an error or is missing. If no error is found in the received RRC-SDU, the UE-BCFE successfully receives and decodes the RRC-SDU (Step 64). Otherwise, as in the present case, the UE-BCFE discards the entire received RRC-SDU (Step 62) comprising 9 TBs and waits the repetition rate to receive the next RRC-SDU (Step 63). This process continues until the UE-BCFE receives nine (9) consecutive TBs which are correct.
There are two areas of concern with this type of method for receiving the RRC-SDU from the UTRAN. The first area is in the latency of proper/correct reception, which results in reduced performance of system functions requiring system information and or increased reception, thereby reducing radio resource efficiency. The second is when the UE L1 is required to repeatedly receive, decode and process all TBs in the RRC-SDU each time there is an error, this results in high processing and battery costs.
Therefore, there exists a need for an improved UMTS TDD or FDD system.